Zoom lens

ABSTRACT

An inner-focusing zoom lens that includes multi groups of lens pieces, namely, the first lens group or the leading lens group of positive refractivity, the second lens group of negative refractivity, and the remaining trailing groups of positive refractivity, as a whole. At least one group of positive refractivity among the trailing groups includes two or more negative lens pieces, at least one of which is connected on its surface to another lens piece to form a duplicated composite lens so that the junction between two of them functions to diverge incident beams. Assuming now that a sum of the refractivities of all the junctions of the composite lenses can be expressed as Σφ=Σ|(N1−N2)/R| where N1 and N2 are refractivities that substances before and after the junction of the composite lenses respectively have, R is a radius of curvature of the junction, ft is a focal length of the comprehensive lens optics of the zoom lens at the telephoto end.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application of U.S. patent application Ser. No.12/318,515, filed on Dec. 30, 2008, and hereby incorporated in itsentirety by reference, which claimed priority to Japanese PatentApplication No. 2008-004557, filed Jan. 11, 2008, and Japanese PatentApplication No. 2008-004558, filed Jan. 11, 2008, under 35 U.S.C. §119,and which are hereby incorporated in their entireties by reference.

FIELD OF THE INVENTION

The present invention relates to inner-focusing or rear-focusingtelephotography zoom lenses, and more particularly, to zoom lensessuitable for 35-mm cameras, video cameras, electronic still cameras, andso forth that are of approximately 4.3 to 5.7 in variable power ratioand that are capable of attaining enhanced optical performancesthroughout the entire ranges of both power ratio and objective distance.

The present invention is especially directed to the zoom lenses thathave merely a single group of lens pieces among other groups utilizedfor the inner-focusing or the rear-focusing to well compensate forvaried spherical aberration at the telephoto end during the focusing.

BACKGROUND ART

In the prior art, it is well known that some zoom lenses are adapted tosimply displace the leading group of lens pieces closest to a photoshotsubject for the focusing, which may be referred to as a ‘front lensfocusing system’. With such a front lens focusing system, switching afocusing mode to the Automated forces the large heavy lens pieces tomove instantaneously, resulting in an unsatisfactory rapidity.

Additional types of the focusing system, which are known as‘inner-focusing’ and ‘rear-focusing’ have been developed in the artwhich enable rapid focusing by virtue of the reduced dimensions of thefocusing lens groups.

With such inner-focusing and rear-focusing, however, their rapidfocusing ability is a tradeoff of more largely varied aberration, and asa result of the focusing, it becomes hard to compensate adequately forthe aberration varied so much.

In a specific type of the zoom lens, which is for telephoto shootingwith a field angle 2ω of less than 40 degrees at the wide-angle end, apositive lens piece(s) in the first lens group has its convex surfacefaced toward the image plane while a negative lens piece(s) closest tothe photoshot subject in the second lens group has its objective surfaceflattened or convexed in shape and faced toward the photoshot subject,so as to reduce variations in spherical aberration at the telephoto end,thereby facilitating the compensation, which is a tradeoff ofconsiderable difficulties in adjusting and controlling the variedcurvature of the image plane at the wide-angle end.

For instance, one typical inner-focusing zoom lens already disclosedconsists of five groups of lens pieces, including their respectiveoptical properties, i.e., of positive, negative, positive, positive, andnegative refractivities, respectively (see Patent Document 1 listedbelow).

Another zoom lens coping with the aforementioned disadvantage in the artis of six groups of lens pieces where only the fifth succeeding to thefirst or the leading group of them is displaced for the focusing (seePatent Document 2 listed below).

Still another typical zoom lens in the prior art is of six groups oflens pieces, namely, the ones respectively having positive, negative,positive, negative, positive, and negative refractivities, and the sixthserving as the primary focusing lens along with the fourth behave asfloating lens during the focusing for a shift from long distance zoomingto short distance zooming (see Patent Document 3 listed below).

PATENT DOCUMENT 1

Japanese Patent Publication of Unexamined Application No. 2005-292338

PATENT DOCUMENT 2

Japanese Patent Publication of Unexamined Application No. H10-133107

PATENT DOCUMENT 3

Japanese Patent Publication of Unexamined Application No. 2000-47107

The zoom lens as disclosed in Patent Document 1 has a problem ofsignificant variation in curved image plane at the wide-angle end due toa negative lens piece closest to the photoshot subject in the secondlens group that has its surface closer to the subject shaped in concave.

In the zoom lens as disclosed in Patent Document 2, the first or theleading to the fourth of the lens groups underdevelop the variedspherical aberration during the focusing for the shift from the longdistance zooming to the short distance zooming; however, the fifth lensgroup permits the variations in spherical aberration to be overdone andprevalent by means of connecting a single negative lens piece andanother lens piece into a composite lens with its junction serving todiverge incident beams, so as to countervail the variations in thespherical aberration in the lens optics, as a whole. Configured in thismanner, however, the zoom lens fails to sufficiently adjust the variedspherical aberration as desired in the comprehensive lens optics,especially, at the telephoto end, due to the insufficient divergingeffects at the junction of the composite lenses.

Patent Document 2 also teaches the fifth and the fourth of the lensgroups behave in the floating manner for the focusing. This isespecially for adjusting and controlling both the curved image plane atthe wide-angle end and the varied spherical aberration at the telephotoend. In contrast with the one that carries out the focusing simplyrelying on the inner-focusing system, however, this prior art embodimentbecomes more complicated in structure because of additional couplingcomponents to a lens barrel to cope with the floating.

According to the disclosure of Patent Document 3, the first to thefourth of the lens groups underdevelop the varied spherical aberration,and instead, the fifth overturns the same during the focusing, whichpermit the variations in spherical aberration to be reduced in the lensoptics, as a whole. However, the negative lens of the composite lensinsufficiently diverges the incident beam thereon to satisfactorilycompensate for the varied spherical aberration at the telephoto end.Moreover, the teachings about the focusing where the fourth and the sixof the lens groups behave in the floating manner bring about anotherproblem of the more complicated structure due to the coupling componentsadded to the lens barrel to conduct the floating.

During the focusing for the shift from the long distance zooming to theshort distance zooming, in general, the zoom lens is prone tounderdevelop the variations in spherical aberration unless it isspecifically modified to address the desired reduction in displacementof the focusing lens groups or modified in some other ways, and thistendency is conspicuous especially at the telephoto end. As to the zoomlenses designed specifically for the telephoto shooting where a focallength is as long as 400 mm, degradation in optical performance isconsiderable during the focusing for the short distance zooming.

The present invention is made to overcome the aforementioneddisadvantages in the prior art where the zoom lenses employing thefocusing system such as inner-focusing, the rear-focusing, or the like,allow for rapid focusing in contrast with the front lens focusing systembut compromise with difficulty in well compensating for the variedaberration, and accordingly, it is an object of the present invention toprovide a zoom lens that has merely a single group of lens pieces amongother groups utilized for the inner-focusing or the rear-focusing towell compensate for the varied spherical aberration at the telephoto endduring the focusing.

SUMMARY OF THE INVENTION

In an aspect of the present invention, there is provided aninner-focusing zoom lens that includes multi groups of lens pieces,namely, the first lens group or the leading lens group of positiverefractivity, the second lens group of negative refractivity, and theremaining trailing groups of positive refractivity, as a whole. At leastone group of positive refractivity among the trailing groups includestwo or more negative lens pieces, at least one of which is connected onits surface to another lens piece to form a duplicated composite lens sothat the junction between two of them functions to diverge incidentbeams. Assuming now that a sum of the refractivities of all thejunctions of the composite lenses can be expressed as Σφ=Σ|(N1−N2)/R|where N1 and N2 are refractivities that substances before and after thejunction of the composite lenses respectively have, R is a radius ofcurvature of the junction, ft is a focal length of the comprehensivelens optics of the zoom lens at the telephoto end, and φt=1/ft is therefractivity of the comprehensive lens optics at the telephoto end, therequirements as defined in the following formula are satisfied:

2<Σφ/φt<10  (1)

The inner-focusing zoom lens of the present invention can be describedin more detailed as follows:

The zoom lens is comprised of at least five of the groups of lenspieces, namely, the first lens group or the leading lens group ofpositive refractivity, the second lens group of negative refractivity,the third lens group of positive refractivity, the fourth lens group ofpositive refractivity, and the fifth lens group of negative refractivityall arranged in this order on the closest to the photoshot subjectforemost basis, and the fourth lens group includes two or more negativelens pieces, at least one of which is connected on its surface toanother lens piece into a duplicated composite lens so that the junctionbetween two of them functions to diverge incident beams.

The zoom lens is modified to include at least six of the groups of lenspieces, namely, the first lens group or the leading lens group ofpositive refractivity, the second lens group of negative refractivity,the third lens group of positive refractivity, the fourth lens group ofpositive refractivity, the fifth lens group of positive refractivity,and the six lens group of negative refractivity all arranged in thisorder on the closest to the photoshot subject foremost basis, and thefifth lens group includes two or more negative lens pieces, at least oneof which is connected on its surface to another lens piece into aduplicated composite lens so that the junction between two of themfunctions to diverge incident beams.

The zoom lens in the present aspect is characterized in that therearmost lens group closest to the image plane are used for thefocusing.

The zoom lens in the present aspect is also characterized in that therearmost lens of positive refractivity and closest to the image plane isused for the focusing.

The zoom lens is also characterized in that at least one group ofpositive refractivity among the third lens group and all the succeedinglens groups includes a triplicated composite lens ofnegative-positive-negative power configuration of three of the lenspieces.

In another aspect of the present invention, the zoom lens is comprisedof at least five of the groups of lens pieces, namely, the first lensgroup or the leading lens group of positive refractivity, the secondlens group of negative refractivity, the third lens group of positiverefractivity, the fourth lens group of positive refractivity, and thefifth lens group of negative refractivity all arranged in this order onthe closest to the photoshot subject foremost basis, or is modifiablycomprised of at least six of the groups of lens pieces, namely, thefirst lens group or the leading lens group of positive refractivity, thesecond lens group of negative refractivity, the third lens group ofpositive refractivity, the fourth lens group of positive refractivity,the fifth lens group of positive refractivity, and the six lens group ofnegative refractivity all arranged in this order on the closest to thephotoshot subject foremost basis. In either of such zoom lenses, thefirst lens group at least includes one negative lens piece and two ormore positive lens pieces, and the first lens group provides opticalproperties as expressed by the following formulae:

40<vd1<55  (2)

20<vd2<35  (3)

where vd1 is an Abbe number of the negative lens piece(s) in the firstlens group, and vd2 is the Abbe number of the positive lens piece(s) inany one of the lens groups of positive refractivity succeeding to thefirst lens group.

In still another aspect of the present invention, the inner-focusingzoom lens that does not conduct the floating focusing includes multigroups of lens pieces, namely, the first lens group or the leading lensgroup of positive refractivity, the second lens group of negativerefractivity, and the remaining trailing groups of positiverefractivity, as a whole. The second lens group includes a meniscusnegative lens having its convex surface faced toward the photoshotsubject, and another composite lens having negative and positive lenspieces connected to one another, and the second lens group providesoptical properties as expressed by the following formulae:

1<R/f(wide)<8  (4)

2ω(wide)<40  (50)

where R is a radius of curvature of an objective surface of the foremostlens piece in the second lens group, f(wide) is a focal length of thecomprehensive lens optics at the wide-angle end, and ω(wide) is a halffield angle of the comprehensive lens optics at the wide-angle end.

The zoom lens in the present aspect is characterized in that at leastone group of positive refractivity among the third lens group and allthe succeeding lens groups includes a triplicated composite lens ofnegative-positive-negative power configuration of three of the lenspieces.

The zoom lens is comprised of the first lens group or the leading lensgroup of positive refractivity, the second lens group of negativerefractivity, and the remaining trailing groups of positiverefractivity, as a whole. At least one group of positive refractivityamong the trailing groups includes two or more negative lens pieces, atleast one of which is connected on its surface to another lens piece toform a duplicated composite lens so that the junction between two ofthem functions to diverge incident beams. Assuming now that a sum of therefractivities of all the junctions of the composite lenses can beexpressed as Σφ=Σ|(N1−N2)/R| where N1 and N2 are refractivities thatsubstances before and after the junction of the composite lensesrespectively have, R is a radius of curvature of the junction, f(tele)is a focal length of the comprehensive lens optics of the zoom lens atthe telephoto end, and φ(tele)=1/f(tele) is the refractivity of thecomprehensive lens optics at the telephoto end, the following formula isgiven:

2<Σφ/φ(tele)<10  (6)

The zoom lens can be modified to be characterized in that at least onegroup of positive refractivity among the third lens group and all thesucceeding lens groups includes a triplicated composite lens ofnegative-positive-negative power configuration of three of the lenspieces.

Details of the Required Components

The zoom lens of the present invention satisfies the conditions as givenby the following formula:

2<Σφ/φt<10  (1)

with the assumptions that the sum of the refractivities of all thejunctions of the composite lenses can be expressed as Σφ=Σ|(N1−N2)/R|where N1 and N2 are the refractivities that substances before and afterthe junction of the composite lenses respectively have, R is the radiusof curvature of the junction, ft is the focal length of thecomprehensive lens optics of the zoom lens at the telephoto end, andφt=1/ft is the refractivity of the comprehensive lens optics at thetelephoto end.

The formula (1) defines a range of the sum of the refractivities of allthe junctions of the composite lenses in any of the lens group(s) (onlythe 4th in this case) including two or more negative lenses and one ormore composite lenses, relative to the refractivity of the comprehensivelens optics. As the sum of the refractivities of the junctions exceedsthe lower limit, the zoom lens tends to lose more the effects of varyingthe spherical aberration to be overdone and prevalent, resulting in thecomprehensive lens optics hardly countervailing the sphericalaberration, especially, at the telephoto end.

As the sum exceeds the upper limit defined in the formula (1), the zoomlens tends to have the spherical aberration excessively overdone andprevalent during the fourth lens group's focusing for the long distancezooming, resulting in the zoom lens hardly countervailing the sphericalaberration throughout the entire variable power range unless the lensgroup(s) displaced ahead of the fourth lens group, especially, the thirdlens group adjusts the spherical aberration to be emphaticallyunderdeveloped.

In an embodiment of the present invention, a zoom lens comprising atleast five of the groups of lens pieces, namely, the first lens group orthe leading lens group of positive refractivity, the second lens groupof negative refractivity, the third lens group of positive refractivity,the fourth lens group of positive refractivity, and the fifth lens groupof negative refractivity all arranged in this order on the closest tothe photoshot subject foremost basis, or comprising at least six of thegroups of lens pieces, namely, the first lens group or the leading lensgroup of positive refractivity, the second lens group of negativerefractivity, the third lens group of positive refractivity, the fourthlens group of positive refractivity, the fifth lens group of positiverefractivity, and the six lens group of negative refractivity allarranged in this order on the closest to the photoshot subject foremostbasis,

the first lens group at least includes one negative lens piece and twoor more positive lens pieces, and the first lens group provides opticalproperties as expressed by the following formulae:

40<vd1<55  (2)

20<vd2<35  (3)

where vd1 is an Abbe number of the negative lens piece(s) in the firstlens group, and vd2 is the Abbe number of the positive lens piece(s) inany one of the lens groups of positive refractivity succeeding to thefirst lens group.

The formula (2) defines a range of the Abbe number of the negative lenspiece in the first lens group. As the Abbe number exceeds the lowerlimit, the zoom lens tends to encounter difficulties in wellcompensating for chromatic aberration of magnification of the g-line andcomatic aberration in an area below the g-line, especially, at thetelephoto end. As the Abbe number exceeds the upper limit, the zoom lenstends to get hard to well compensate for the chromatic aberration ofmagnification of the c-line, especially, at the telephoto end.

The formula (3) defines a range of the Abbe number of the positive lenspiece(s) in any one of the lens group(s) of positive refractivitysucceeding to the aperture stop.

As the Abbe number exceeds the lower limit, the zoom lens tends toencounter difficulties in well compensating for the chromatic aberrationof magnification of the g-line, especially, at the telephoto end. As theAbbe number exceeds the upper limit, the zoom lens tends to get hard towell compensate for axial chromatic aberration of the c-line and thechromatic aberration of magnification of the same, especially, at thetelephoto end.

The zoom lens according to the present invention applies the formula (2)to well compensate for the chromatic aberration of magnification of theg-line, especially at the telephoto end. With an adjustment by simplyapplying the formula (2), it becomes hard instead to satisfactorilycorrect the chromatic aberration of magnification of the c-line,especially at the telephoto end. Hence, such adjustment along with theapplication of the formula (3) enables the zoom lens to successfullycorrect the chromatic aberration of magnification of the c-line as well.

In another embodiment of the present invention, the inner-focusing zoomlens comprises at least five of the groups of lens pieces, namely, thefirst lens group or the leading lens group of positive refractivity, thesecond lens group of negative refractivity, the third lens group ofpositive refractivity, the fourth lens group of positive refractivity,and the fifth lens group of negative refractivity all arranged in thisorder on the closest to the photoshot subject foremost basis; the fourthlens group including two or more negative lens pieces, at least one ofwhich is connected on its surface to another lens piece into aduplicated composite lens so that the junction between two of themfunctions to diverge incident beams. This zoom lens is advantageous inthat its entire length can be downsized. To depart from theabove-defined requirements would undesirably increase the dimensions ofthe zoom lens.

In another embodiment of the invention, the inner-focusing zoom lenscomprises at least six of the groups of lens pieces, namely, the firstlens group or the leading lens group of positive refractivity, thesecond lens group of negative refractivity, the third lens group ofpositive refractivity, the fourth lens group of positive refractivity,the fifth lens group of positive refractivity, and the sixth lens groupof negative refractivity all arranged in this order on the closest tothe photoshot subject foremost basis; the fifth lens group including twoor more negative lens pieces, at least one of which is connected on itssurface to another lens piece into a duplicated composite lens so thatthe junction between two of them functions to diverge incident beams.This zoom lens is preferred in that its entire length can be downsizedand that it can well compensate for astigmatism throughout the entirezoom range. To departing from the above-defined requirements would leadto the zoom lens resulting in undesirably increased dimensions as wellas difficulties in flattening the image plane throughout the entire zoomrange.

In the zoom lens of the present invention, it is desirable that therearmost lens group closest to the image plane primarily conducts thefocusing. This is desirable in successfully reducing the variations inthe spherical aberration, as a whole, in the comprehensive lens optics.When the rearmost lens group closest to the image plane is not usedprimarily to conduct the focusing, the zoom lens is unable to increase aheight of the incident beams upon the lens group including at least twonegative lens pieces and the composite lens during the focusing for theshort distance zooming, and consequently, it fails to reduce thevariations in the spherical aberration in the comprehensive lens optics.

In the zoom lens of the present invention, it is advantageous when therearmost lens group of positive refractivity and closest to the imageplane primarily conducts the focusing. This is advantageous in that thevariations in the spherical aberration in the comprehensive lens opticscan be reduced. When the rearmost lens group of positive refractivityand closest to the image plane is not used primarily to conduct thefocusing, the zoom lens is unable to increase a height of the incidentbeams upon the lens group including two negative lens pieces and thecomposite lens during the focusing for the short distance zooming, andtherefore, it fails to reduce the variations in the spherical aberrationin the comprehensive lens optics.

The best mode to adjust and control the varied spherical aberrationduring the focusing, is when at least one group of positive refractivityamong the third lens group and all the succeeding lens groups includes atriplicated composite lens of negative-positive-negative powerconfiguration of three of the lens pieces. When this is not the case,the zoom lens encounters significantly frequented and increasedhigher-order aberration and adverse sensitivity that means considerabledevelopment of various types of the aberration due to manufacturingtolerance, eventually resulting in inability to design for fineproducts.

In an inner-focusing zoom lens that does not conduct the floatingfocusing and that comprises multi groups of lens pieces, namely, thefirst lens group or the leading lens group of positive refractivity, thesecond lens group of negative refractivity, and the remaining trailinggroups of positive refractivity, as a whole,

the second lens group includes a meniscus negative lens having itsconvex surface faced toward the photoshot subject, and a composite lenshaving negative and positive lens pieces connected to one another, andthe second lens group provides optical properties as expressed by thefollowing formulae:

1<R/f(wide)<8  (4)

2ω(wide)<40  (5)

where R is a radius of curvature of an objective surface of the foremostlens piece in the second lens group, f(wide) is a focal length of thecomprehensive lens optics at the wide-angle end, and ω(wide) is a halffield angle of the comprehensive lens optics at the wide-angle end. Theformula 1<R/f(wide)<8 set forth above provides a range of the radius ofcurvature of an objective surface of the negative lens piece closest tothe photoshot subject in the second lens group, relative to the focallength at the wide-angel end. As the radius of curvature exceeds theupper limit, it is hard to well compensate for the variations incurvature of field during the focusing, especially, at the wide-angleend. As the radius of curvature exceeds the lower limit, the desiredanti-aberration effectiveness imposed on the negative lens piece closestto the photoshot subject must be taken over and countervailed by anothernegative lens piece(s) in the same lens group, which cannot be attainedwith the triplicated composite power configuration of three of the lenspieces in the second lens group.

The formula 2ω(wide)<40 set forth above provides a range of the fieldangle at the wide-angle end.

As the field angle exceeds the upper limit, the zoom lens loses itsmerits as a telephoto-shooting zooming lens.

The formula 2<Σφ/φ(tele)<10 provides a range of the sum of therefractivities of all the junctions of the composite lenses disposedalong with two or more negative lens pieces in the same lens group,relative to the refractivity of the comprehensive lens optics at thetelephoto end.

As the sum of the refractivities exceeds the upper limit, the zoom lenstends to have the spherical aberration excessively overdone andprevalent during such a lens group's focusing for the long distancezooming, resulting in the zoom lens hardly countervailing the sphericalaberration throughout the entire variable power range unless any one(s)displaced ahead of that lens group, especially, the third lens groupadjusts the spherical aberration to be emphatically underdeveloped.

As the sum of the refractivities exceeds the lower limit, that lensgroup tends to lose more the effects of varying the spherical aberrationto be overdone and prevalent, resulting in the comprehensive lens opticshardly countervailing the spherical aberration, especially, at thetelephoto end.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view illustrating a first embodiment of a zoomlens in accordance with the present invention.

FIG. 2 is a sectional view illustrating a second embodiment of the zoomlens in accordance with the present invention.

FIG. 3 is a sectional view illustrating a third embodiment of the zoomlens in accordance with the present invention.

FIG. 4 is a sectional view illustrating a fourth embodiment of the zoomlens in accordance with the present invention.

FIG. 5 is a sectional view illustrating a fifth embodiment of the zoomlens in accordance with the present invention.

FIG. 6 is a sectional view illustrating a sixth embodiment of the zoomlens in accordance with the present invention.

FIG. 7 depicts aberration at the wide-angle end under an assumption ofthe infinitely far imaging plane in the first exemplary zoom lens.

FIG. 8 depicts the aberration at the wide-angle end under anotherassumption of 1.6 meters in distance from the leading or foremost lenspiece to a photoshot subject in the first exemplary zoom lens.

FIG. 9 depicts aberration at the intermediate focal length under theassumption of the infinitely far imaging plane in the first exemplaryzoom lens.

FIG. 10 depicts the aberration at the intermediate focal length underthe assumption of 1.6 meters in distance from the leading or foremostlens piece to the photoshot subject in the first exemplary zoom lens.

FIG. 11 depicts aberration at the telephoto end under the assumption ofthe infinitely far imaging plane in the first exemplary zoom lens.

FIG. 12 depicts the aberration at the telephoto end under the assumptionof 1.6 meters in distance from the leading or foremost lens piece to thephotoshot subject in the first exemplary zoom lens.

FIG. 13 depicts aberration at the wide-angle end under the assumption ofthe infinitely far imaging plane in the second exemplary zoom lens.

FIG. 14 depicts the aberration at the wide-angle end under theassumption of 1.6 meters in distance from the leading or foremost lenspiece to the photoshot subject in the second exemplary zoom lens.

FIG. 15 depicts aberration at the intermediate focal length under theassumption of the infinitely far imaging plane in the second exemplaryzoom lens.

FIG. 16 depicts the aberration at the intermediate focal length underthe assumption of 1.6 meters in distance from the leading or foremostlens piece to the photoshot subject in the second exemplary zoom lens.

FIG. 17 depicts aberration at the telephoto end under the assumption ofthe infinitely far imaging plane in the second exemplary zoom lens.

FIG. 18 depicts the aberration at the telephoto end under the assumptionof 1.6 meters in distance from the leading or foremost lens piece to thephotoshot subject in the second exemplary zoom lens.

FIG. 19 depicts aberration at the wide-angle end under the assumption ofthe infinitely far imaging plane in the third exemplary zoom lens.

FIG. 20 depicts the aberration at the wide-angle end under theassumption of 1.6 meters in distance from the leading or foremost lenspiece to the photoshot subject in the third exemplary zoom lens.

FIG. 21 depicts aberration at the intermediate focal length under theassumption of the infinitely far imaging plane in the third exemplaryzoom lens.

FIG. 22 depicts the aberration at the intermediate focal length underthe assumption of 1.6 meters in distance from the leading or foremostlens piece to the photoshot subject in the third exemplary zoom lens.

FIG. 23 depicts aberration at the telephoto end under the assumption ofthe infinitely far imaging plane in the third exemplary zoom lens.

FIG. 24 depicts the aberration at the telephoto end under the assumptionof 1.6 meters in distance from the leading or foremost lens piece to thephotoshot subject in the third exemplary zoom lens.

FIG. 25 depicts aberration at the wide-angle end under the assumption ofthe infinitely far imaging plane in the fourth exemplary zoom lens.

FIG. 26 depicts the aberration at the wide-angle end under theassumption of 1.6 meters in distance from the leading or foremost lenspiece to the photoshot subject in the fourth exemplary zoom lens.

FIG. 27 depicts aberration at the intermediate focal length under theassumption of the infinitely far imaging plane in the fourth exemplaryzoom lens.

FIG. 28 depicts the aberration at the intermediate focal length underthe assumption of 1.6 meters in distance from the leading or foremostlens piece to the photoshot subject in the fourth exemplary zoom lens.

FIG. 29 depicts aberration at the telephoto end under the assumption ofthe infinitely far imaging plane in the fourth exemplary zoom lens.

FIG. 30 depicts the aberration at the telephoto end under the assumptionof 1.6 meters in distance from the leading or foremost lens piece to thephotoshot subject in the fourth exemplary zoom lens.

FIG. 31 depicts aberration at the wide-angle end under the assumption ofthe infinitely far imaging plane in the fifth exemplary zoom lens.

FIG. 32 depicts the aberration at the wide-angle end under theassumption of 1.6 meters in distance from the leading or foremost lenspiece to the photoshot subject in the fifth exemplary zoom lens.

FIG. 33 depicts aberration at the intermediate focal length under theassumption of the infinitely far imaging plane in the fifth exemplaryzoom lens.

FIG. 34 depicts the aberration at the intermediate focal length underthe assumption of 1.6 meters in distance from the leading or foremostlens piece to the photoshot subject in the fifth exemplary zoom lens.

FIG. 35 depicts aberration at the telephoto end under the assumption ofthe infinitely far imaging plane in the fifth exemplary zoom lens.

FIG. 36 depicts the aberration at the telephoto end under the assumptionof 1.6 meters in distance from the leading or foremost lens piece to thephotoshot subject in the fifth exemplary zoom lens.

FIG. 37 depicts aberration at the wide-angle end under the assumption ofthe infinitely far imaging plane in the sixth exemplary zoom lens.

FIG. 38 depicts the aberration at the wide-angle end under theassumption of 1.6 meters in distance from the leading or foremost lenspiece to the photoshot subject in the sixth exemplary zoom lens.

FIG. 39 depicts aberration at the intermediate focal length under theassumption of the infinitely far imaging plane in the sixth exemplaryzoom lens.

FIG. 40 depicts the aberration at the intermediate focal length underthe assumption of 1.6 meters in distance from the leading or foremostlens piece to the photoshot subject in the sixth exemplary zoom lens.

FIG. 41 depicts aberration at the telephoto end under the assumption ofthe infinitely far imaging plane in the sixth exemplary zoom lens.

FIG. 42 depicts the aberration at the telephoto end under the assumptionof 1.6 meters in distance from the leading or foremost lens piece to thephotoshot subject in the sixth exemplary zoom lens.

DETAILED DESCRIPTION OF THE INVENTION

Zoom lenses according to the present invention, including theirrespective variations and modifications are adapted to conduct thefocusing such as inner-focusing, rear-focusing, and the like, morebriskly and quickly in comparison with the front lens focusing system,and the improved zoom lenses of groups of lens pieces merely displace asingle group of lens pieces to well compensate for variations inspherical aberration, especially, at the telephoto end.

Embodiment 1

f = 72.0785~390.0019 FNo. = 4.11~5.78 (Data on Surfaces) r d nd vd  0(Objective Surface) ∞ ∞  1 425.3905 2.3000 1.80420 46.50  2 105.03878.1955 1.49700 81.61  3 −562.0044 0.3000  4 110.7871 7.3867 1.4970081.61 −1221.5706 Variable  6 256.4914 1.5000 1.48749 70.44 38.56315.8780  8 −89.5171 0.9000 1.48749 70.44  9 45.0811 3.4531 1.80610 33.2710 120.9491 Variable 11 74.0490 3.7000 1.67003 47.20 12 −131.1456 1.924613 −47.6423 1.3000 1.80610 40.73 14 −280.5770 0.2000 15 43.7230 3.50001.72000 50.34 16 64.0768 4.3536 17 (Aperture Stop) ∞ Variable 18−141.9867 3.5000 1.80518 25.46 19 −51.7664 0.1500 20 48.6209 1.30001.83400 37.34 21 24.6183 10.7880 1.51680 64.20 22 −27.6249 1.20001.84666 23.78 23 96.4484 2.2370 24 81.0305 4.3305 1.84666 23.78 25−68.8511 Variable 26 191.9351 1.2000 1.77250 49.62 27 47.7663 2.5284 28482.3384 4.0000 1.84666 23.78 29 −76.8478 5.0000 30 −69.1358 1.50001.83481 42.72 31 200.0000 Variable 32 (Image Plane) ∞ (Various Data)Zoom Ratio 5.411 WIDE MIDDLE TELE f 72.0785 167.1066 390.0019 FNo. 4.115.56 5.78 2ω° 33.212 14.454 6.234 Image Height 21.633 21.633 21.633 FullLens Length 225.142 275.999 311.667 Variable Interval (Focused at theInfinity-Point) d0 ∞ ∞ ∞ d5 1.5000 54.4500 114.8693 d10 55.5123 30.01661.5000 d17 16.8647 10.0484 1.5000 d25 21.7305 14.7668 1.0000 BF 46.909084.0920 110.1720 Variable Interval (Focused with 1.6-meter Distance tothe Subject) d0 1374.86 1324.00 1288.33 d5 1.5000 54.4500 114.8693 d1055.5123 30.0166 1.5000 d17 16.8647 10.0484 1.5000 d25 23.3970 18.984217.1782 BF 45.2430 79.8750 93.9940 (Data on the Zoom Lens Groups) GroupInitial Surface f 1 1 210.0756 2 6 −61.8149 3 11 165.5535 4 18 60.9734 526 −63.5770 (Values of the Primary Term in the Formulae) Formula (1)9.68 Formula (2) 46.50 Formula (3) 23.78

Embodiment 2

f = 72.0702~387.8665 FNo. = 4.15~5.74 (Data on the Surfaces) r d nd vd 0 (Objective Surface) ∞ ∞  1 464.3037 2.3000 1.80400 46.58  2 117.27767.6304 1.49700 81.61  3 −668.1523 0.3000  4 125.0743 6.9036 1.4970081.61  5 −1086.8029 Variable  6 400.0000 1.7000 1.51680 64.20  7 62.98432.9660  8 −209.8881 1.3000 1.48749 70.21  9 43.1221 2.5662 1.75520 27.5110 70.2788 Variable 11 77.1859 3.2583 1.58913 61.18 12 −142.4720 2.483413 −43.6774 1.5000 1.72342 37.95 14 −360.1644 0.2000 15 48.1790 4.16041.75520 27.51 16 102.9396 3.0000 17 (Aperture Stop) ∞ Variable 18221.3497 1.5000 1.76182 26.55 19 55.0393 3.5987 20 176.6014 4.94031.51633 64.15 21 −40.6879 0.2000 22 132.6269 5.9583 1.56883 56.34 23−33.2235 1.3000 1.78590 44.19 24 −266.0050 0.2000 25 52.1984 4.06871.49700 81.61 26 −458.0671 Variable 27 103.5193 1.5000 1.83481 42.72 2843.0987 2.3941 29 1915.8683 3.7371 1.76182 26.55 30 −44.9612 1.50001.48749 70.21 31 −66.5655 3.1137 32 −50.2801 1.2000 1.80400 46.58 33200.0000 Variable 34 (Image Plane) ∞ (Various Data) Zoom Ratio 5.382WIDE MIDDLE TELE f 72.0702 167.0620 387.8665 FNo. 4.15 5.12 5.74 2ω°33.214 14.390 6.260 Image Height 21.633 21.633 21.633 Full Lens Length230.089 283.557 320.126 Variable Interval (Focused at theInfinity-Point) d0 ∞ ∞ ∞ d5 7.7179 76.4777 132.8660 d10 62.9882 33.71141.5000 d17 15.9264 10.2597 1.5000 d26 20.8883 14.7132 1.5000 BF 47.089072.9160 107.2810 Variable Interval (Focused with 1.6-meter Distance tothe Subject) d0 1369.91 1316.44 1279.87 d5 7.7179 76.4777 132.8660 d1062.9882 33.7114 1.5000 d17 15.9264 10.2597 1.5000 d26 22.3449 19.003015.1222 BF 45.6330 68.6270 93.6590 (Data on the Zoom Lens Groups) GroupInitial Surface f 1 1 232.6486 2 6 −71.5603 3 11 165.8567 4 18 56.5968 527 −57.0465 (Values of the Primary Term in the Formulae) Formula (1)2.53 Formula (2) 46.58 Formula (3) 27.51

Embodiment 3

f = 71.7730~291.9632 FNo. = 4.59~5.79 (Data on the Surfaces) r d nd vd 0 (Objective Surface) ∞ ∞  1 75.0392 5.6833 1.48749 70.44  2 617.32940.2000  3 88.8879 1.4000 1.78590 43.93  4 44.0278 8.0931 1.49700 81.61 5 526.7875 Variable  6 275.5840 1.0000 1.77250 49.62  7 32.9367 2.9002 8 −251.0357 1.0000 1.48749 70.44  9 25.3841 4.0675 1.67270 32.17 10135.9493 Variable 11 (Aperture Stop) ∞ 2.0000 12 29.8854 5.0241 1.4874970.44 13 −268.4437 2.0014 14 −34.6079 1.0000 1.77250 49.62 15 −94.7884Variable 16 −29.8468 2.7103 1.72825 28.32 17 −23.8487 0.1000 18 70.84481.0000 1.80610 33.27 19 28.8852 8.2977 1.48749 70.44 20 −20.2504 1.00001.80610 33.27 21 −42.2605 0.1000 22 37.7570 3.5000 1.77250 49.62 23199.3442 Variable 24 97.6915 1.0000 1.62041 60.34 25 26.3176 2.9258 26−153.4459 2.5953 1.84666 23.78 27 −40.0547 1.2000 1.77250 49.62 28200.0000 Variable 34 (Image Plane) ∞ (Various Data) Zoom Ratio 4.068WIDE MIDDLE TELE f 71.7730 140.0942 291.9632 FNo. 4.59 5.60 5.79 2ω°32.824 17.054 8.246 Image Height 21.633 21.633 21.633 Full Lens Length175.925 206.840 235.878 Variable Interval (Focused at Infinity-Point) d0∞ ∞ ∞ d5 1.6500 30.4176 65.7475 d10 28.9039 15.7723 3.6150 d15 20.349314.9521 7.8202 d23 13.6315 9.7660 1.5000 BF 52.5920 77.1330 98.3970Variable Interval (Focused with 1.6-meter Distance to the Subject) d01424.07 1393.16 1364.12 d5 1.6500 30.4176 65.7475 d10 28.9039 15.77233.6150 d15 20.3493 14.9521 7.8202 d23 14.3597 11.3889 6.3196 BF 51.864075.5100 93.5770 (Data on the Zoom Lens Groups) Group Initial Surface f 11 139.7971 2 6 −49.1963 3 11 193.8488 4 16 36.0311 5 24 −39.7982 (Valuesof the Primary Term in the Formulae) Formula (1) 7.81 Formula (2) 43.93Formula (3) 28.32

Embodiment 4

f = 72.0790~388.0549 FNo. = 3.85~6.35 (Data on the Surfaces) r d nd vd 0 (Objective Surface) ∞ ∞  1 241.2170 2.3000 1.83400 37.34  2 111.07976.7649 1.49700 81.61  3 −695.2799 0.3000  4 137.5395 5.8335 1.4970081.61  5 −754.2861 Variable  6 350.0000 1.5000 1.62280 57.06  7 40.82844.5778  8 −86.6512 1.2000 1.48749 70.44  9 47.9402 3.3989 1.80610 33.2710 266.2338 Variable 11 171.9973 3.3732 1.65844 50.85 12 −112.61531.9131 13 −42.7454 1.2000 1.83481 42.72 14 −261.9302 0.2000 15 74.04023.8458 1.60311 60.69 16 −179.3158 5.0000 17 (Aperture Stop) ∞ Variable18 −414.6225 3.1568 1.78472 25.72 19 −78.3244 3.4069 20 78.3956 1.50001.79950 42.34 21 34.8786 10.1423 1.48749 70.44 22 −34.8808 1.50001.84666 23.78 23 −96.8311 0.3338 24 60.7270 4.5000 1.72000 50.34 25−392.9783 Variable 26 132.9111 1.2000 1.80420 46.50 27 36.5287 2.8896 28−489.4854 3.9259 1.84666 23.78 29 −36.8054 1.2000 1.83481 42.72 30200.0000 Variable 31 (Image Plane) ∞ (Various Data) Zoom Ratio 5.384WIDE MIDDLE TELE f 72.0790 167.0937 388.0549 FNo. 3.85 5.26 6.35 2ω°33.130 14.400 6.248 Image Height 21.633 21.633 21.633 Full Lens Length235.118 276.672 320.213 Variable Interval (Focused at theInfinity-Point) d0 ∞ ∞ ∞ d5 2.5000 46.8297 92.3228 d10 54.0017 26.17962.0000 d17 32.9868 25.7167 19.6391 d25 16.6794 11.7738 3.0000 BF 53.788091.0100 128.0890 Variable Interval (Focused with 1.6-meter Distance tothe Subject) d0 1364.88 1323.33 1279.79 d5 2.5000 46.8297 92.3228 d1054.0017 26.1796 2.0000 d17 32.2739 23.6712 12.9801 d25 17.3923 13.81939.6590 BF 53.7880 91.0100 128.0890 (Data on the Zoom Lens Groups) GroupInitial Surface f 1 1 185.9118 2 6 −64.1404 3 11 199.4687 4 18 49.3767 526 −45.6959 (Values of the Primary Term in the Formulae) Formula (1)7.47 Formula (2) 37.34 Formula (3) 25.72

Embodiment 5

f = 70.7231~388.1393 FNo. = 4.05~5.87 (Data on the Surfaces) r d nd vd 0 (Objective Surface) ∞ ∞  1 341.4865 2.3000 1.80420 46.50  2 100.07498.6788 1.49700 81.61  3 −580.6182 0.3000  4 102.6378 7.9544 1.4970081.61  5 −1349.2717 Variable  6 250.0000 1.7000 1.63854 55.45  7 38.50995.5546  8 −113.5820 1.3000 1.48749 70.44  9 50.7413 3.1884 1.80610 33.2710 154.1035 Variable 11 83.8353 3.7221 1.63854 55.45 12 −166.1224 1.837513 −44.9779 1.3078 1.83481 42.72 14 232.9722 0.2000 15 59.8407 3.97201.84666 23.78 16 −354.6810 2.0000 17 (Aperture Stop) ∞ Variable 18204.1703 1.3000 1.84666 23.78 19 34.6621 6.4963 1.64769 33.84 20−98.0309 Variable 21 −317.9391 1.3000 1.84666 23.78 22 36.5447 10.87071.63854 55.45 23 −25.8401 1.3000 1.80610 33.27 24 −60.5610 0.2000 2559.5597 4.6131 1.84666 23.78 26 −533.7403 Variable 27 63.6049 1.20001.72000 50.34 28 31.8746 3.6172 29 −235.1399 4.0756 1.78472 25.72 30−37.4552 1.2000 1.80420 46.50 31 237.3893 Variable 32 (Image Plane) ∞(Various Data) Zoom Ratio 5.488 WIDE MIDDLE TELE f 70.7231 167.0889388.1393 FNo. 4.05 5.32 5.87 2ω° 33.848 14.468 6.256 Image Height 21.63321.633 21.633 Full Lens Length 235.174 278.686 320.220 Variable Interval(Focused at the Infinity-Point) d0 ∞ ∞ ∞ d5 2.5000 49.1230 100.5475 d1051.3031 21.4622 2.0000 d17 18.8055 10.7526 0.9318 d20 1.4049 7.748412.6161 d26 18.9608 15.5224 4.1107 BF 62.0110 93.8890 119.8250 VariableInterval (Focused with 1.6-meter Distance to the Subject) d0 1364.821321.31 1279.78 d5 2.5000 49.1230 100.5475 d10 51.3031 21.4622 2.0000d17 18.8055 10.7526 0.9318 d20 1.4049 7.7484 12.6161 d26 19.8428 18.283214.1726 BF 61.1290 91.1280 109.7630 (Data on the Zoom Lens Groups) GroupInitial Surface f 1 1 186.6475 2 6 −56.9423 3 11 164.6565 4 18 197.93755 21 63.1960 6 27 −53.3835 (Values of the Primary Term in the Formulae)Formula (1) 4.73 Formula (2) 46.50 Formula (3) 23.78

Embodiment 6

f = 72.0562~388.0927 FNo. = 4.11~5.79 (Data on the Surfaces) r d nd vd 0 (Objective Surface) ∞ ∞  1 322.4599 2.3000 1.80420 46.50  2 91.01039.2192 1.49700 81.61  3 −569.0188 0.3000  4 93.4615 8.6041 1.49700 81.61 5 −1008.031 Variable  6 198.4362 1.7000 1.61800 63.39  7 37.6062 8.4309 8 −70.0748 1.3000 1.48749 70.44  9 52.5435 3.2219 1.80610 33.27 10190.1372 Variable 11 73.6767 3.8864 1.61800 63.39 12 −176.6382 2.1013 13−42.3439 1.7886 1.83481 42.72 14 196.0411 0.2000 15 69.6402 4.50001.84666 23.78 16 −174.3032 2.0000 17 (Aperture Stop) ∞ Variable 18−5925.0049 1.3000 1.84666 23.78 19 39.5747 7.5004 1.59551 39.22 20−56.4431 Variable 21 174.5724 1.3000 1.84666 23.78 22 47.3325 8.87341.61800 63.39 23 −33.6393 1.3000 1.80610 33.27 24 −147.2232 0.2000 2581.2810 4.0000 1.84666 23.78 26 −208.9178 Variable 27 145.4029 1.20001.61800 63.39 28 41.1585 2.8866 29 −934.5306 4.0410 1.74077 27.76 30−46.3879 1.2000 1.80420 46.50 31 390.3333 Variable 32 (Image Plane) ∞(Various Data) Zoom Ratio 5.386 WIDE MIDDLE TELE f 72.0562 167.0619388.0927 FNo. 4.11 5.18 5.79 2ω° 33.610 14.530 6.268 Image Height 21.63321.633 21.633 Full Lens Length 240.127 284.816 330.165 Variable Interval(Focused at the Infinity-Point) d0 ∞ ∞ ∞ d5 2.5000 47.2958 92.4906 d1046.1612 18.4655 2.0000 d17 17.1294 10.9430 6.3591 d20 2.8519 11.581113.0322 d26 21.9339 18.2572 2.5000 BF 66.1963 94.9192 130.4291 VariableInterval (Focused with 1.6-meter Distance to the Subject) d0 1359.871315.18 1269.84 d5 2.5000 47.2958 92.4906 d10 46.1612 18.4655 2.0000 d1717.1294 10.9430 6.3591 d20 1.9768 8.4604 1.9920 d26 22.8090 21.377913.5402 BF 66.1963 94.9192 130.4291 (Data on the Zoom Lens Groups) GroupInitial Surface f 1 1 172.0317 2 6 −52.5524 3 11 189.0866 4 18 228.11245 21 69.8075 6 27 −65.9427 (Values of the Primary Term in the Formulae)Formula (1) 4.04 Formula (2) 46.50 Formula (3) 23.78

Detailed Description of Embodiment 1 to 4

The preferred embodiments disclosed as Embodiment 1 to Embodiment 4 havefive groups of lens pieces, namely, the first or foremost lens group ofpositive refractivity, the second lens group of negative refractivity,the third lens group of positive refractivity, the fourth lens group ofpositive refractivity, and the fifth lens group of negativerefractivity, and in order to alter the variable power from thewide-angle view to the telephoto view, at least the first, the third,the fourth, the fifth of the lens groups are moved toward the photoshotsubject so that the first and the second of the lens groups to move tohave an increased interval therebetween, the second and the third ofthem to move to have the decreased interval therebetween, the third andthe fourth of them to move to have the reduced interval therebetween,and the fourth and the fifth of them to move to have the reducedinterval therebetween.

The aperture stop is disposed in position closer to either the imageplane or the photoshot subject in the third lens group, and it isdisplaced along with the lens pieces of the third lens group.

In order to focus from the long distance zooming to the short distancezooming, there are two ways, namely, the rear-focusing (as set forth inEmbodiment 1 to Embodiment 3) where the rearmost lens group closest tothe image plane (the fifth in this case) is displaced, and theinner-focusing (as set forth in Embodiment 4) where the rearmost lensgroup of positive refractivity and closest to the image plane isdisplaced. Either of the inner- and rear-focusing systems can attainmore brisk and quick focusing, compared with the front lens focusing,and employing these focusing systems enables the zoom lenses to bedownsized without degradation in ensuring a sufficient amount ofspherical light. A displacement of the lens groups relative to theidentical photoshot subject becomes greater as the focal lengthincreases.

The lens group(s) (the fourth in this case) of positive refractivityamong the third lens group and all the succeeding lens groups has two ormore negative lens pieces, and at least one of the negative lens pieceshas its one major surface connected to another lens piece to form thecomposite lens of which junction serves to diverge beams incidentthereon. In general, the zoom lens is prone to underdevelop variationsin spherical aberration unless it is specifically modified in structureto reduce the displacement of the lens groups used for the focusing. Thezoom lens according to the present invention also has the first to thethird of the lens groups adapted to underdevelop the varied sphericalaberration. With the fourth lens group of positive refractivity designedto have two negative lens pieces at least one of which is the compositelens having the beam diverging junction, the fourth lens group causesthe varied spherical aberration to be overdone and prevalent, therebycountervailing the varied spherical aberration, as a whole, in thecomprehensive lens optics, especially at the telephoto end.

The overdone variations in the spherical aberration by the fourth lensgroup is by virtue of excessively developing the spherical aberration asa result of inducing the beams to be incident upon the fourth lens groupat a higher point during the short distance zooming relative to the longdistance zooming. In this way, the lens groups dedicated to the focusingdoes not have its performance design limited to the rear-focusing buthave a choice of the inner-focusing by the rearmost lens group ofpositive refractivity and closest to the image plane (as in Embodiment4).

However, any of the focusing lens groups other than the one includingtwo negative lens pieces at least one of which is the composite lensserving to diverge beams at its junction with the remaining componentlens piece(s) cannot induce the incident beams thereon to enter at thehigher point during the short distance focusing, and therefore, thevaried spherical aberration cannot be reduced.

To satisfy requirements of the composite lenses, it is desirable thatthe negative lens component should be made of glass showing a highrefractive index while the positive lens component is made of glassshowing a low refractive index, so as to enhance a radius of curvatureat the junction between them. In the present invention, however, therequirements are defined to meet those given in the formula (1).

The best mode for the focusing with the reduced variations in thespherical aberration desirably includes a triplicated composite lens ofnegative-positive-negative power configuration of three lens pieces inat least one lens group (in this case, the fourth) of positiverefractivity among the third and the remaining succeeding ones. Althougha single lens is also capable of inducing the spherical aberration to beoverdone, such a mono-lens configuration is liable to cause high-orderaberration as well as enhanced sensitivity, which resultantly obstructsthe way of enhancing the radius of curvature.

Detailed Description of Embodiment 5 and Embodiment 6

The preferred embodiments disclosed as Embodiment 5 and Embodiment 6have six groups of lens pieces, namely, the first or foremost lens groupof positive refractivity, the second lens group of negativerefractivity, the third lens group of positive refractivity, the fourthlens group of positive refractivity, the fifth lens group of positiverefractivity, and the six lens group of negative refractivity, and inorder to alter the variable power from the wide-angle view to thetelephoto view, at least the first, the third, the fourth, the fifth andthe sixth of the lens groups are moved toward the photoshot subject sothat the first and the second of the lens groups to move to have anincreased interval therebetween, the second and the third of them tomove to have the decreased interval therebetween, the third and thefourth of them to move to have the reduced interval therebetween, andthe fourth and the fifth of them to move to have the increased intervaltherebetween, and the fifth and the sixth of them to move to have thereduced interval therebetween. The second lens group may keep staticduring altering the power ratio.

The aperture stop is disposed in position closer to either the imageplane or the photoshot subject in the third lens group, and it isdisplaced along with the lens pieces of the third lens group.

In order to focus from the long distance zooming to the short distancezooming, there are two ways, namely, the rear-focusing (as set forth inEmbodiment 5) where the rearmost lens group closest to the image plane(the sixth in this case) is displaced, and the inner-focusing (as setforth in Embodiment 6) where the rearmost lens group of positiverefractivity and closest to the image plane is displaced.

During altering the variable power from the wide-angle view to thetelephoto view, the fourth lens group and the fifth lens group aredisplaced to come farther from each other. In this way, the zoom lens issatisfactorily compensated for astigmatism.

The fifth lens group includes two or more negative lens pieces one ofwhich is a component of the composite lens that has its junction servingto diverge beams, thereby inducing the spherical aberration to beoverdone and prevalent in the fifth lens group during the focusing so asto countervail the varied spherical aberration in the comprehensive lensoptics, especially, at the telephoto end.

Moreover, the fourth lens group includes the additional composite lensthat has a junction between the component lens pieces serving to divergebeams incident thereon, thereby functioning as an auxiliary effect ofinducing the overdone spherical aberration. In this way, the fourth lensgroup in addition to the fifth cooperatively work to reduce the variedspherical aberration during the focusing.

1. A zoom lens comprising at least five groups of lens pieces, namely, afirst lens group or the leading lens group of positive refractivity, asecond lens group of negative refractivity, a third lens group ofpositive refractivity, a fourth lens group of positive refractivity, anda fifth lens group of negative refractivity all arranged in this orderon the closest to the photoshot subject foremost basis, or comprising atleast six groups of lens pieces, namely, a first lens group or theleading lens group of positive refractivity, a second lens group ofnegative refractivity, a third lens group of positive refractivity, afourth lens group of positive refractivity, a fifth lens group ofpositive refractivity, and a sixth lens group of negative refractivityall arranged in this order on the closest to the photoshot subjectforemost basis, wherein the first lens group at least includes onenegative lens piece and two or more positive lens pieces, and the firstlens group provides optical properties as expressed by the followingformulae:40<vd1<55  (2)20<vd2<35  (3) where vd1 is an Abbe number of the negative lens piece(s)in the first lens group, and vd2 is the Abbe number of the positive lenspiece(s) in any one of the lens groups of positive refractivitysucceeding to the first lens group.
 2. In an inner-focusing zoom lensthat does not conduct the floating focusing and that comprises multigroups of lens pieces, namely, the first lens group or the leading lensgroup of positive refractivity, the second lens group of negativerefractivity, and the remaining trailing groups of positiverefractivity, as a whole, the second lens group includes a meniscusnegative lens having its convex surface faced toward the photoshotsubject, and a composite lens having negative and positive lens piecesconnected to one another, and the second lens group provides opticalproperties as expressed by the following formulae:1<R/f(wide)<8  (4)2ω(wide)<40  (5) where R is a radius of curvature of an objectivesurface of the foremost lens piece in the second lens group, f(wide) isa focal length of the comprehensive lens optics at the wide-angle end,and ω(wide) is a half field angle of the comprehensive lens optics atthe wide-angle end.
 3. The zoom lens according to claim 2, comprisingthe first lens group or the leading lens group of positive refractivity,the second lens group of negative refractivity, and the remainingtrailing groups of positive refractivity, as a whole, at least one groupof positive refractivity among the trailing groups including two or morenegative lens pieces, at least one of which is connected on its surfaceto another lens piece to form a duplicated composite lens so that thejunction between two of them functions to diverge incident beams;assuming now that a sum of the refractivities of all the junctions ofthe composite lenses can be expressed as Σφ=Σ|(N1−N2)/R| where N1 and N2are refractivities that substances before and after the junction of thecomposite lenses respectively have, R is a radius of curvature of thejunction, f(tele) is a focal length of the comprehensive lens optics ofthe zoom lens at the telephoto end, and φ(tele)=1/f(tele) is therefractivity of the comprehensive lens optics at the telephoto end, therequirement as defined in the following formula are satisfied:2<Σφ/φ(tele)<10  (6)
 4. The zoom lens according to claim 2, wherein atleast one group of positive refractivity among the third lens group andall the succeeding lens groups includes a triplicated composite lens ofnegative-positive-negative power configuration of three of the lenspieces.